The present invention relates to a vibratory plate used for an audio-electrical instrument.
It has heretofore been very difficult to regenerate evenly, with one speaker only, sound having a scope extending from low frequencies of 30 - 50 Hz to high frequencies of 15000 - 20000 Hz or more. Yet such a frequency range is generally said to be necessary for high fidelity loud speakers.
Heretofore, so-called double cone-type loud speakers have been used for that purpose. These have combined a small diameter cone for high frequency sound reproduction with a large diameter cone for low frequency sound reproduction. Alternatively, a plurality of separate speakers consisting of a large diameter speaker for low frequencies and a small diameter speaker for high frequencies has been adopted. However, mutual interference often takes place in a connecting portion between the low frequency zone and the high frequency zone, causing large and small waves in the frequency characteristics. When a network is used for dividing frequencies, satisfactory damping of low frequencies cannot be obtained. When independent amplifiers are used for low and for high frequencies, the cost of the equipment rises substantially. Accordingly, there are many problems in use, design and manufacture.
An object of the present invention is to provide a vibratory plate which is capable of regenerating evenly a broad scope of frequency from low to high without using a plurality of vibratory plates.
Another object of the present invention is to provide a vibratory plate for an audio electrical instrument having a large .sqroot.E/.rho. and a proper value of internal loss which is one of the most important characteristics of vibratory plates.
Still another object of the present invention is to provide a vibratory plate for an audio-electrical instrument without creating large and small waves having frequency characteristics considered to be due to resonance, and which has excellent capability in separating sounds.
Still another object of the present invention is to provide a vibratory plate for an audio-electrical instrument which is unlikely to be subjected to strain at the time of its formation.
Other objects of the present invention will become apparent from the following description.
The present invention provides a vibratory plate for an audio-electrical instrument comprising paper made of pulp having a maximum beating degree of 300 cc of freeness when measured by the Canadian standard freeness test, and chopped carbon fibers having a Young's modulus of at least about 8000 kg/mm.sup.2, said pulp and (chopped) carbon fibers being mixed evenly with each other.
The term "freeness" in this specification means Canadian standard freeness, measured by the method referred to as "Tappi Standard" T-227m-58, as designated by TAPPI (Technical Association of the Pulp and Paper Industry) of the United States of America.